The present invention relates to a radiation-curable organopolysiloxane composition or, more particularly, to a radiation-curable organopolysiloxane or silicone composition which provides a coating layer on a substrate surface fully cured by irradiation with actinic rays to be freed from the problem of surface migration of the silicone.
Conventionally, several types of organopolysiloxane compositions are known as those curable by irradiation with actinic rays. They include, for example, the compositions curable by the mechanism of the addition reaction induced by the irradiation with light between an organopolysiloxane having vinyl groups bonded to the silicon atoms and an organohydrogenpolysiloxane having hydrogen atoms directly bonded to the silicon atoms disclosed in Japanese Patent Kokai No. 47-32072 and No. 53-48198 and the compositions curable by the reaction in the presence of a photosensitizer between an organopolysiloxane having mercapto groups bonded to the silicon atoms and an organopolysiloxane having vinyl groups bonded to the silicon atoms disclosed in Japanese Patent Publications No. 54-6523 and No. 57-34318 and Japanese Patent Kokai No. 54-48854 and No. 54-50067.
These compositions are, however, not quite satisfactory in properties when they are used in some applications such as the use in release papers because curing of the silicone composition on the surface is sometimes incomplete to cause migration of the silicone toward a body in contact with the silicone-coated surface. That is, there are several disadvantages such as a change of the releasing property in the lapse of time and the migration of the silicone to the layer of the pressure-sensitive adhesive in contact therewith owing to the incomplete cure by the irradiation with light when the composition is used as a very thin coating film applied to the surface of a paper as the substrate of release papers for temporary protection.
Therefore, there have been several proposals with an object to overcome these deficiencies by the improvement of the curability including increase of the content of the functional groups in the organopolysiloxanes and increase of the amount of the photosensitizer compound, but these measures are not profitable because of some disadvantages accompanying thereto including the adverse deterioration of releasing performance and evolution of an unpleasant odor to greatly decrease the practicability of the methods.